This invention relates to a light activated semiconductor device, and more particularly to a light activated thyristor which has a high dv/dt capability.
A light activated thyristor which has the function of switching from the forward blocked state into the conductive state by being irradiated with light is constructed of at least four layers of p-n-p-n, a pair of main electrodes lying in ohmic contact with both the outer layers of the four layers, and a portion to be irradiated with light to serve as a trigger. As compared with an electrically-gated thyristor, the light activated thyristor has such advantages (1) that since a main circuit and a gate circuit can be electrically isolated, and the gate circuit can be simplified, and (2) that it is immune to noise due to electromagnetic induction. Therefore, the development of light activated thyristors for high voltage which can demonstrate these advantages best has been proceeding at a rapid rate recently.
A light activated semiconductor device of the type described above is disclosed in U.S. Pat. No. 3,893,153. As one of problems in this device, it is mentioned that the more the dV/dt capability is raised, the more the light ignition sensitivity deteriorates. That is, the dV/dt capability and the light ignition sensitivity are mutually contradictory requirements.